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United States Patent |
5,676,472
|
Solomon
,   et al.
|
October 14, 1997
|
Rotary labyrinth seal
Abstract
A rotary seal is located in a gap between an inner surface and an outer
surface. A radial bearing allows the inner and outer surfaces to rotate
relative to each other. A radial barrier includes a plurality of annular
outward-pointing flanges attached to the inner surface interleaved with a
plurality of annular inward-pointing flanges attached to the outer
surface. The flanges may be angled and have an upturned lip located at an
inner edge of each flange. The radial seal may include a magnet. A robotic
arm has a first housing with a top surface and an aperture therein. A
shaft extends up through the aperture, and there is a gap between the
shaft and an inner edge of the aperture. A splash guard may extend over
said gap, and an indentation in said top surface may at least partially
surround the gap.
Inventors:
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Solomon; Todd (Los Gatos, CA);
Thomas; Donald J. (San Jose, CA)
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Assignee:
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Smart Machines (San Jose, CA)
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Appl. No.:
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500124 |
Filed:
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July 10, 1995 |
Current U.S. Class: |
384/607; 277/347; 277/410; 277/419; 384/133; 384/480 |
Intern'l Class: |
F16C 033/78; F16C 033/82 |
Field of Search: |
384/607,144,480,133
277/80
|
References Cited
U.S. Patent Documents
2779640 | Jan., 1957 | Jones | 384/480.
|
4348067 | Sep., 1982 | Tooley | 384/144.
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4527915 | Jul., 1985 | Ikariishi et al. | 384/489.
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4605233 | Aug., 1986 | Sato | 277/80.
|
Other References
Ferrofluidics Corporation, "Ferrofluidic Metric Vacuum Rotary
Feedthroughs," (Information Bulletin). (1995).
Rigaku Corporation, "Rigaku/Magnetic Rotary Seal Unit--Rotary Feedthrough,
RMS Seris," pp. 1-10. (1995).
|
Primary Examiner: Footland; Lenard A.
Attorney, Agent or Firm: Fish & Richardson, P.C.
Claims
What is claimed is:
1. A radial seal comprising:
an inner surface;
an outer surface, the inner and outer surfaces separated by a gap;
a radial bearing located in the gap for allowing the inner and outer
surfaces to rotate relative to each other; and
a radial barrier located in said gap, the barrier including a plurality of
angled annular outward-pointing flanges attached to the inner surface
interleaved with a plurality of annular inward-pointing flanges attached
to said outer surface, each of said flanges having an upturned lip at an
inner edge thereof.
2. The radial seal of claim 1 wherein the flange located nearest the radial
bearing is angled downwardly.
3. The radial seal of claim 2 wherein the flanges other than the flange
located nearest the radial bearing are angled upwardly.
4. The radial seal of claim 1 further comprising a magnet located in the
gap.
5. A radial seal comprising:
an inner surface;
an outer surface, the inner and outer surfaces separated by a gap;
a radial bearing located in the gap for allowing the inner and outer
surfaces to rotate relative to each other;
a magnet located in the gap; and
a radial barrier located in the gap, the barrier including a plurality of
annular outward-pointing flanges attached to the inner surface interleaved
with a plurality of annular inward-pointing flanges attached to the outer
surface.
6. The radial seal of claim 5 wherein the magnet is attached to a flange.
7. A robotic arm comprising:
a housing having a top surface with an aperture therein and an indentation
at least partially surrounding the aperture;
a shaft extending up through the aperture, there being a gap between the
shaft and the housing;
a radial bearing located in the gap for allowing the shaft to rotate
relative to the housing; and
a radial barrier located in the gap, the barrier including a plurality of
annular outward-pointing flanges attached to the shaft interleaved with a
plurality of annular inward-pointing flanges attached to the housing.
8. The robotic arm of claim 7 further comprising a splash guard connected
to the shaft and extending over the aperture.
9. A robotic arm comprising:
a housing having a top surface with an aperture therein
a shaft extending up through the aperture, there being a gap between the
shaft and the housing;
a splash guard connected to the shaft and extending over the aperture;
a radial bearing located in the gap for allowing the shaft to rotate
relative to the housing;
a radial barrier located in the gap, the barrier including a plurality of
annular outward-pointing flanges attached to the shaft interleaved with a
plurality of annular inward-pointing flanges attached to the housing.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
Reference is made to the concurrently filed applications, Ser. No.
08/500,428, filed Jul. 10, 1995, entitled DIRECT DRIVEN ROBOT, and Ser.
No. 08/500,429, filed Jul. 10, 1995, entitled ROBOTIC JOINT USING METAL
BANDS, assigned to the assignee of the present application, each of which
is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates generally to seals for rotating shafts, and
more particularly to labyrinth seals and splash guards to protect a
bearing and/or rotary seal between rotating shafts.
Material handling robots are used in automated manufacturing of integrated
circuits, flat panel displays, and other precision-made products. Many of
these products require near-sterile handling of extremely fragile and
expensive materials, such as semiconductor wafers, during the
manufacturing process. In semiconductor manufacturing, raw materials and
in-process workpieces must be kept extremely clean; the circuit paths
etched on the workpieces are so small (e.g., 0.18-10 microns) that minute
particles can contaminate the paths and render the finished circuit
inoperative. Therefore, sealed, ultra-clean robots are used to move the
materials accurately, gently, and precisely, within a clean room,
preventing contamination or damage to the materials which could occur
through human contact or handling. However, such robots must not generate
particles of metal, leak chemicals, or produce other materials which could
contaminate a wafer or other substrate.
Further, robots must move precisely to specific points in space to carry
out various manufacturing steps. Because wafers, flat panels, and other
substrates are extremely fragile and expensive, all robot movements must
be gentle and precise. "Backlash," or play in the mechanical components of
the robot, must be minimized to ensure accurate movement and to prevent
damage to an object on the robot.
In addition, some manufacturing processes are carried out in a vacuum, or
require hazardous chemicals. Robots must be vacuum-compatible, and able to
handle materials in vacuum and corrosive environments which are hostile to
humans.
In many manufacturing applications, as shown in FIG. 1, a rotating shaft 7
extends into a chamber 10, such as an ultraclean room or a vacuum chamber.
Shaft 7 is connected to some instrument 8, such as a robotic arm, a
stirrer, a substrate support, or an electrode, in chamber 10. Because
shaft 7 is driven by a motor at normal atmospheric pressure, the joint
between shaft 7 and the chamber walls must be sealed by a rotary seal 5 to
prevent atmosphere from entering chamber 10.
Seal unit 5 includes a housing 12 which surrounds shaft 7, and rotatable
joint 14. Joint 14 might be a bearing, such as a ball bearing, or joint 14
could be seal, such as a rubber O-ring. A conventional manner of sealing
the gap between rotatable shafts is a rubber O-ring. A more recent type of
seal is the magnetic fluid, or "ferrofluid" seal. As shown in FIG. 1, in
the magnetic fluid rotary seal, a ring of magnetic liquid 18 fills the gap
between the moving shaft 7 and the stationary housing 12. Magnetic liquid
18 is held in place by powerful magnets 16, thereby sealing the gap while
allowing rotation of shaft 7 virtually without abrasive friction. There
is, however, a substantial viscous drag torque due to the viscosity of
magnetic liquid 18.
There are two dangers associated with the use of rotary seal unit 5. First,
particles might escape seal unit 5 and contaminate chamber 10. A total
failure of the seal, under atmospheric pressure, can cause catastrophic
blow-out of the magnetic liquid into chamber 10. This is disastrous in
ultra-clean manufacturing processes such as semiconductor wafer
fabrication. Second, particles from chamber 10 might enter and damage seal
unit 5.
In view of the foregoing, it is an object of the invention to provide a
rotary seal unit from which contaminates do not escape.
It is another object of the invention to provide a rotary seal which
protects the internal joint from contaminants in the chamber.
SUMMARY OF THE INVENTION
The present invention is directed to a rotary seal. The seal is located in
a gap between an inner surface and an outer surface. There is a radial
bearing located in the gap for allowing the inner and outer surfaces to
rotate relative to each other. A radial barrier is located in the gap. The
radial barrier includes a plurality of annular outward-pointing flanges
attached to the inner surface interleaved with a plurality of annular
inward-pointing flanges attached to the outer surface.
The flanges in the radial seal may be angled and have an upturned lip
located at an inner edge of each flange. The radial seal may include a
magnet.
The invention is also directed to robotic arm with a first housing having a
top surface and an aperture therein. A shaft extends up through the
aperture, and there is a gap between the shaft and an inner edge of the
aperture. A splash guard may extend over the gap, and an indentation in
the top surface may at least partially surround the gap.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic cross-sectional view of a prior art rotary seal.
FIG. 2 is a schematic perspective view of a robot arm.
FIG. 3 is a schematic partial cross-section of the shoulder joint in a
robot arm.
FIG. 4 is a schematic cross-section of a labyrinth seal with a magnet.
FIG. 5 is a schematic perspective view with partial cut-away of a labyrinth
seal module.
FIG. 6 is a schematic cross-section of an angled labyrinth seal.
FIG. 7 is a view of FIG. 3 in which the outer shaft has been cut away.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in FIG. 2, a robot 20 is constructed to mimic the lateral freedom
of motion of a human arm. Robot 20 has a base 22 with an attached movable
arm 24. Arm 24 includes an upper arm 26, a forearm 28, and a hand or end
effector 30. Upper arm 26 is connected to base 24 by a rotatable shoulder
32, forearm 28 is connected to upper arm 26 by a rotatable elbow 34; and
hand 30 is connected to forearm 28 by a rotatable wrist 36.
Base 22 contains motors to drive several rotatable shafts. One rotatable
shaft connects directly to upper arm 26 and controls the rotation of
shoulder 32. Another shaft connects to forearm 28 by a pulley (see FIG. 7)
and controls the rotation of elbow 34.
For many applications, such as semiconductor fabrication, movable arm 24 of
robot 20 must manipulate objects in an ultraclean environment or vacuum
chamber. However, base 22 is usually operated at normal atmospheric
pressure. Therefore, the joint between arm 24 and base 22 must be sealed
to prevent atmosphere from entering the vacuum chamber.
As shown in FIG. 3, according to the present invention, base 22 includes a
circular housing 40 surrounding a shaft 45. In gap 50 between the inner
wall of housing 40 and the outer surface of shaft 45 there is a joint 55
which allows shaft 45 to rotate along its primary or central axis relative
to the housing 40. Joint 55 may also act as a seal. For example, joint 55
may be a magnetic fluid rotary seal which includes multiple magnetic
liquid rings. Since each additional ring increases the pressure
differential the seal can sustain without rupturing, a sufficient number
of rings will allow base 22 to be maintained at atmospheric pressure while
arm 24 operates in a vacuum.
Above joint 55, in gap 50 between housing 40 and shaft 45, there is a
labyrinth seal 57. Labyrinth seal 57 will be explained in detail with
reference to FIG. 4. Continuing with FIG. 3, beneath housing 40 is a
bellows 75, which is formed like a cylindrical metal accordion.
Since movable arm 24 operates in an ultraclean chamber, any leakage of
sealing material or bearing material from joint 55 into the chamber must
be prevented. For example, droplets of magnetic liquid can escape from a
magnetic fluid seal and contaminate the vacuum chamber. As another
example, particles may be ground off a rotating bearing and contaminate
the ultraclean environment.
It is also possible for joint 55 to be contaminated by material from the
vacuum chamber side. For example, sputtered materials may lodge in the
seal, or cleaning solution may be spilled into gap 50. When such a
contaminant enters joint 55, it may, for example, dilute the magnetic
fluid and destroy the joint.
Also, if cleaning solution is splashed on bellows 75, then metal particles
carried by the cleaning solution will lodge on the pleats of bellows 75.
When bellows 75 compresses and the pleats fold together, the lodged
particles will grind and damage the bellows.
The top surface 60 of base 22 has a depression to catch liquid and prevent
it from entering gap 50. Preferably, the depression is a circular moat 65
located around shoulder 32. A splash guard 70 is mounted directly to the
bottom of shoulder 32, surrounding shaft 45. Splash guard 70 is formed as
a circular disk 72 with a downwardly angled edge 73. Circular disk 72
projects out beyond shoulder 26 and downturned edge 72 drops slightly
below top surface 60 into moat 65. Moat 65 is deep and wide enough to hold
about four cubic inches of liquid. Assuming that top surface 60 of base 22
has a diameter of sixteen inches, then the moat has an inner diameter of
6.5 inches, an outer diameter of 8 inches, and a depth of 0.35 inches.
Splash guard 70 may be firmly attached to either the bottom of arm 26, or
directly to shaft 45, but in either case it will rotate with shaft 45.
Moat 65 is cut out to be clear in any possible position of arm 36 so that
splash guard 70 does not affect the rotation of shaft 45.
If liquid is splashed directly on arm 26, then the liquid will run down the
sides of shoulder 32, onto splash guard 70, and into moat 65. The liquid
will collect in moat 65 rather than enter gap 50. For example, if someone
cleaning robot 20 pours alcohol directly on shoulder 32, the alcohol will
pool in moat 65 and not reach seal 55. Pooled liquid in moat 65 may later
be removed by an eyedropper, or it may soak into an absorbent material, or
it may be left to evaporate.
As shown in FIG. 4, a labyrinth seal 80 is located adjacent a joint 85 in
the gap 90 between an inner shaft 87 and an outer shaft 88. Outer shaft 88
may be part of an immobile housing (see also FIG. 3) or the outer shaft
may be another rotating shaft which surrounds the inner shaft (see also
FIG. 6). In either case, joint 85 allows inner shaft 87 to rotate with
respect to outer shaft 88 about axis 92. The joint 85 may be a bearing,
such as a pair of ball bearings, or a seal, such as an O-ring or a
magnetic fluid seal, or a combination of bearings and seals. Joint 85 will
include inner and outer support structures 92 and 94, and seal or bearing
96.
Labyrinth seal 80 generally takes the form of a radial conduit 100 having a
tortuous intrawound path from the exterior of seal 80 to joint 85.
Labyrinth seal 80 includes an outer cylindrical surface 102 having inward
pointing radial flanges 104a, 104b, and an inner cylindrical surface 106
having outward radial flanges 108a, 108b. The inward pointing flanges
104a, 104b are interleaved with the outward pointing flanges 108a, 108b to
form conduit 100. Although FIG. 4 shows exactly four flanges, the
invention can apply to two or more flanges.
The flanges of labyrinth seal 80 act as a barrier to particles that escape
joint 85. For example, if joint 85 is a magnetic fluid seal, then magnetic
fluid that leaks from joint 85 may be captured in conduit 100. The greater
the number of flanges, the more tortuous the conduit 100, and the more
likely that particles will be trapped. In addition, in the event of a
catastrophic failure of joint 85, labyrinth seal 80 can prevent
contaminants from entering chamber 10. This is because the intrawound path
100 provides a large volume in which contaminants can accumulate.
In general, the ratio between the width of gap 90 and the distance between
adjacent flanges should be about 3:1. The flanges should project into gap
90 sufficiently to overlap, and there should not be any straight path from
joint 85 to the open area of gap 90. Preferably, the flanges project about
3/4 of the distance to the opposite wall.
Labyrinth seal 80 may be formed as an integral part of shafts 87 and 88, or
it may be manufactured as a separate module which is dropped into gap 90.
If labyrinth seal 80 is an integral part of shafts 87 and 88, then
outward-pointing flanges 108a, 108b could be attached directly to inner
shaft 87 which would serve as the inner surface 104. Similarly,
inward-pointing flanges 106a, 106b could be attached directly to outer
shaft 88.
In the preferred embodiment, as shown in FIG. 5, labyrinth seal 80 is a
separate module 120. Module 120 is dropped into gap 90. The inner wall 122
of module 120 rests on a step 124 in inner shaft 87 and outer wall 126 of
module 120 rests on a step 128 in outer shaft 88. Outward directed flanges
130 and 131 are attached to inner wall 122, and inward directed flange 133
is attached to outer wall 126. After module 120 is inserted into gap 90,
circular clips 135 and 137 are used to clip inner wall 122 to shaft 87 and
outer wall 126 to shaft 88.
As shown in FIG. 4, labyrinth seal 80 may include one or more magnets 110.
In the preferred embodiment, magnet 110, is a radial washer attached to
the uppermost flange (e.g. flange 104b). If joint 80 produces magnetic
particles, then magnet 110 will help prevent those particles from
contaminating the ultraclean environment. For example, if joint 85 is a
magnetic fluid seal, then magnetic liquid which escapes from joint 85 will
be attracted and held by magnet 110, and will be less likely to escape
seal 80.
Labyrinth seal 80 may also be integrated with joint 85 as a single module.
In such an embodiment, the inner and outer walls 122 and 126 would be
attached to the inner and outer support structures 92 and 94,
respectively.
As shown in FIG. 6, the flanges in labyrinth seal 80 may be angled away
from the horizontal. Each flange 140 includes an angled base 142 and an
upturned lip 144. The bases of upper flanges 150 may be angled downward,
whereas the base of the lowest flange 152 may be angled upward. The angled
base and upturned lip structure of flanges 140 help prevent joint 85 from
being contaminated by materials from chamber 10. Specifically, if a liquid
is spilled or poured into gap 90, for example, when equipment is washed
down with solvents, then the liquid will trapped by lip 144 to form a pool
146. In case of an overflow from upper flanges 150, the upward angle of
the base of lowest flange 152 provides additional storage capacity for the
liquid. Eventually, pool 146 will evaporate.
As shown in FIG. 7, base 22 of robot 20 may have a housing 40, an outer
shaft 160 that connects a shoulder motor to upper arm 26, and an inner
shaft 162 that connects an elbow motor to a shoulder pulley 164. Shoulder
pulley 164 runs inside arm 26 and connects to forearm 28. There is a gap
170 between housing 40 and outer shaft 160, and a gap 172 between outer
shaft 160 and inner shaft 162. Labyrinth seals 166 and 168 are positioned
concentrically in gaps 170 and 172, respectively, above joints 174 and
176. More labyrinth seals 178 and 180 may be placed below joints 174 and
176 to provide additional protection for bellows 75.
Other implementations of the invention are contemplated and are within the
scope of the invention.
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